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A photograph of the handheld probe. The motor, translation stage, ultrasonic transducer, and optical fibers are all incorporated in this handheld probe for easy operation. Image courtesy of Yong Zhou.

August 06, 2014 11:01 AM Eastern Daylight Time

WASHINGTON--(BUSINESS WIRE)--A new hand-held device that uses lasers and sound waves may change the
way doctors treat and diagnose melanoma, according to a team of
researchers from Washington University in St. Louis. The instrument,
described in a paper published today in The Optical Society’s (OSA)
journal Optics
Letters, is the first that can be used directly on a patient and
accurately measure how deep a melanoma tumor extends into the skin,
providing valuable information for treatment, diagnosis or prognosis.

Melanoma is the fifth most common cancer type in the United States, and
incidence rates are rising faster than those of any other cancer. It's
also the deadliest form of skin cancer, causing more than 75 percent of
skin-cancer deaths.

The thicker the melanoma tumor, the more likely it will spread and the
deadlier it becomes, says dermatologist Lynn Cornelius, one of the
study's coauthors. Being able to measure the depth of the tumor in vivo
enables doctors to determine prognoses more accurately—potentially at
the time of initial evaluation—and plan treatments and surgeries
accordingly.

The problem is that current methods can't directly measure a patient's
tumor very well. Because skin scatters light, high-resolution optical
techniques don't reach deep enough. "None are really sufficient to
provide the two to four millimeter penetration that's at least required
for melanoma diagnosis, prognosis or surgical planning," says engineer
Lihong Wang, another coauthor on the Optics Letters paper.

Researchers have tried other methods, but they aren't much better.
High-frequency ultrasound doesn't have enough image contrast, and
magnetic resonance imaging and positron emission tomography have
insufficient resolution and require expensive and bulky instruments.

"Any type of tissue diagnosis at this point in time requires taking
tissue out of the person and processing it and looking at it under the
microscope," Cornelius says.

But because taking a biopsy often only involves the removal of a part of
a tumor—when it's in a cosmetically sensitive area, for
instance—provisional measurements of the tumor depth are not always
reliable. If, at the time of excision, the surgeon finds that the tumor
goes deeper than initially thought, the patient may need yet another
surgery.

Recently, researchers including Wang have applied an approach called
photoacoustic microscopy, which can accurately measure melanoma tumors
directly on a patient's skin—thus allowing doctors to avoid uncertainty
in some circumstances.

The technique relies on the photoacoustic effect, in which light is
converted into vibrations. In the case of the new device, a laser beam
shines into the skin at the site of a tumor. Melanin, the skin pigment
that's also in tumors, absorbs the light, whose energy is transferred
into high-frequency acoustic waves. Unlike light, acoustic waves don't
scatter as much when traveling through skin. Tumor cells will produce
more melanin than the surrounding healthy skin cells, and as a result,
the acoustic waves can be used to map the entire tumor with high
resolution. The device has a detector that can then turn the acoustic
signal into a three-dimensional image on a screen.

Wang, Cornelius and their colleagues previously built a similar desktop
device, which shines the laser directly onto the tumor. But so much
light is absorbed that very little penetrates to the tumor's lower
layers. The latest version, however, is not only hand-held, but it also
delivers light around and below the tumor, which generates a bright
image of the tumor's bottom and an accurate measurement of its depth.

The researchers tested their device on both artificial tumors made of
black gelatin and on real ones in live mice, showing that the instrument
could accurately measure the depths of tumors—and do it in living tissue.

Initially, this tool will be mainly used for improving how doctors plan
and prepare for surgeries, Cornelius says. But what's especially
exciting, she adds, is that it can measure a tumor's entire
volume—something that's never been possible with melanoma. If
researchers can determine how the volume relates to cancer outcomes,
then this tool could give doctors a new type of measurement for
diagnosis and prognosis.

The researchers are now conducting further tests with human patients.
The new device will have to prove effective in clinical trials before it
is widely available. But other than that Wang says, the device is
essentially ready for commercialization.

EDITOR’S NOTE: Images are available to members of the media upon
request. Contact Lyndsay Meyer, lmeyer@osa.org.

About Optics Letters

Published by The Optical Society (OSA), Optics Letters offers
rapid dissemination of new results in all areas of optics with short,
original, peer-reviewed communications. Optics Letters covers the
latest research in optical science, including optical measurements,
optical components and devices, atmospheric optics, biomedical optics,
Fourier optics, integrated optics, optical processing, optoelectronics,
lasers, nonlinear optics, optical storage and holography, optical
coherence, polarization, quantum electronics, ultrafast optical
phenomena, photonic crystals, and fiber optics. This journal, edited by
Xi-Cheng Zhang of the University of Rochester and published twice each
month, is where readers look for the latest discoveries in optics. Visit www.OpticsInfoBase.org/OL.

About OSA

Founded in 1916, The Optical Society (OSA) is the leading professional
society for scientists, engineers, students and business leaders who
fuel discoveries, shape real-world applications and accelerate
achievements in the science of light. Through world-renowned
publications, meetings and membership programs, OSA provides quality
research, inspired interactions and dedicated resources for its
extensive global network of professionals in optics and photonics. For
more information, visit www.osa.org.